Re: Warts with SELECT DISTINCT

Bruno Wolff III <bruno@wolff.to> writes:

> On Thu, May 04, 2006 at 00:05:16 -0400,
>   Greg Stark <gsstark@mit.edu> wrote:
> > Bruno Wolff III <bruno@wolff.to> writes:
> > 
> > > > Whereas it shouldn't be hard to prove that this is equivalent:
> > > > 
> > > > stark=> explain select col1 from test group by upper(col1),col1 order by upper(col1);
> > > >                              QUERY PLAN                              
> > > > ---------------------------------------------------------------------
> > > >  Group  (cost=88.50..98.23 rows=200 width=32)
> > > >    ->  Sort  (cost=88.50..91.58 rows=1230 width=32)
> > > >          Sort Key: upper(col1), col1
> > > >          ->  Seq Scan on test  (cost=0.00..25.38 rows=1230 width=32)
> > > > (4 rows)
> > > 
> > > I don't think you can assume that that will be true for any locale. If there
> > > are two different characters that both have the same uppercase version, this
> > > will break things.
> > 
> > No it won't.
> 
> Sure it will, because when you do the group by you will get a different
> number of groups. When grouping by the original characters you will get
> separate groups for characters that have the same uppercase character, where
> as when grouing by the uppercased characters you won't.

But grouping on *both* will produce the same groups as grouping on the
original characters alone.


-- 
greg